P.S. I know this has been discussed before, but the compression_(mode|algorithm) pool options [1] seem completely broken -- With the pool mode set to force, we see that sometimes the compression is invoked and sometimes it isn't. AFAICT, the only way to compress every object is to set bluestore_compression_mode=force on the osd. -- dan [1] http://docs.ceph.com/docs/master/rados/operations/pools/#set-pool-values On Thu, Jun 20, 2019 at 4:33 PM Dan van der Ster <dan@xxxxxxxxxxxxxx> wrote: > > Hi all, > > I'm trying to compress an rbd pool via backfilling the existing data, > and the allocated space doesn't match what I expect. > > Here is the test: I marked osd.130 out and waited for it to erase all its data. > Then I set (on the pool) compression_mode=force and compression_algorithm=zstd. > Then I marked osd.130 to get its PGs/objects back (this time compressing them). > > After a few 10s of minutes we have: > "bluestore_compressed": 989250439, > "bluestore_compressed_allocated": 3859677184, > "bluestore_compressed_original": 7719354368, > > So, the allocated is exactly 50% of original, but we are wasting space > because compressed is 12.8% of original. > > I don't understand why... > > The rbd images all use 4MB objects, and we use the default chunk and > blob sizes (in v13.2.6): > osd_recovery_max_chunk = 8MB > bluestore_compression_max_blob_size_hdd = 512kB > bluestore_compression_min_blob_size_hdd = 128kB > bluestore_max_blob_size_hdd = 512kB > bluestore_min_alloc_size_hdd = 64kB > > From my understanding, backfilling should read a whole 4MB object from > the src osd, then write it to osd.130's bluestore, compressing in > 512kB blobs. Those compress on average at 12.8% so I would expect to > see allocated being closer to bluestore_min_alloc_size_hdd / > bluestore_compression_max_blob_size_hdd = 12.5%. > > Does someone understand where the 0.5 ratio is coming from? > > Thanks! > > Dan _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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